Is two lengths that are of concern if you are in Canada - length of the firearm from rear end to the front end, when firearm configured to fire; then, separate is in relation about minimum length of the barrel, that has been altered from the maker - and added devices, etc., in Canada, do not count for length measurement. Seems to have confused many who think USA laws apply here. See CCC 84 (2) - I am not sure about firearm over-all length - 84 (2) seems to be about how to measure barrel length - might be another place in CCC that talks about measuring firearm length.
Some time ago, I formed the impression that a rifle's barrel was measured in Canada from the closed bolt face to the muzzle - so that includes the chamber and perhaps a mm or two of "air space" related to headspace and bolt face clearance to the barrel rear. Those mm or two have turned out to be very important - at least for some revolver barrels - so "how" to measure, "what" to measure - on which firearm, is kind of important to know. And maybe I got the technique wrong. Is some barrels with a recess that the bolt nose goes into - Remington 700 and some Mausers with "safety breech", for examples - so if you were right at 18" (457 mm) measured from the bolt face to muzzle, the actual barrel would measure slightly longer than that. If you cut that barrel exactly 18" (457 mm) from rear end, would measure "too short" when measuring to the muzzle from the bolt face.
There is a 16 1/2" (420 mm) barrel Ruger 77 in 243 Win here - perfectly legal as a non-restricted, because Ruger made it that way. I am not allowed to maintain one as a "non-restricted" if I saw off a similar barrel, that was made at factory at 22", and I cut it down to 16 1/2" (420 mm) - not allowed - it would become "prohibited", I think - and no way to stay as non-restricted by adding anything to it - I did not make those rules - makes about no sense to me. The factory made one with 16 1/2" (420 mm) barrel is okay; identical sawed off and re-crowned by me with 16 1/2" (420 mm) barrel is not okay. Is mostly why the 243 Win barrel that I shortened and lightened for my wife to use was cut and crowned at 19 inches (483 mm).